1. Field of the Invention
The present invention relates to a holding apparatus for holding a work piece such as a chip part or an IC or the like by so-called vacuum suction or the like and conveying the work piece onto another member to attach the work piece to that member. More particularly, the present invention relates to an illumination method for illuminating a work piece held by a holding member with light to allow detection of a condition of the work piece such as the held position thereof based on an image of the work piece thus illuminated, or relates to a holding apparatus equipped with an illumination apparatus for carrying out that illumination method. The present invention also relates to an inspection system for inspecting the holding state of a work piece when the work piece is held by the aforementioned holding apparatus.
2. Related Background Art
Generally, a chip part such as a resistor or a condenser is picked up from a storing station by a so-called automatic mounting apparatus and mounted on a circuit board. The automatic mounting apparatus is equipped with a holding apparatus for holding a chip part, with which a chip part is actually held and conveyed to the mounting site. In some cases, the chip mounting operation is also carried out by this holding apparatus. Holding of a chip part by this holding apparatus is achieved by, for example, so called vacuum suction. When a chip part is held, positional displacement can occur, in other words, the held position or holding state of the chip part can vary for every individual chip part. In view of this, it is a general practice to pick up an image of the chip part holding state by a camera or the like and change the driving trajectory of the holding apparatus or the position of the circuit board to which the chip part is to be mounted based on the picked up image so as to cope with the positional displacement.
The above-described automatic mounting apparatus is provided with an illumination apparatus for illuminating a chip part used for the aforementioned image pickup operation. An image of the chip part is obtained by illuminating the chip part from the holding apparatus side by means of that illumination apparatus. The image is picked up by a camera that is disposed at a position opposed to the holding apparatus with the chip part between, and the aforementioned image processing is carried out. The illumination apparatuses are roughly categorized into transmissive type and reflective type in accordance with their scheme.
Specific examples of the transmissive type illumination apparatus are disclosed in Japanese Patent Application Laid-Open No. 62-060292 or Japanese Patent Application Laid-Open No. 02-243232. Typically, the holding apparatus is composed of a body portion and a suction nozzle for actually vacuum-sucking a chip part. In these transmissive type illumination apparatuses, a plate-like structure for diffusing and transmitting light is arranged between the suction nozzle and the body portion, and light is projected to the apparatus body side surface of that structure. Thus, the light is guided to a chip part through that structure so that an image of the chip part is formed. In the case of the reflective type illumination apparatus, a chip part or the like is actually illuminated by light and the shape or other properties of the chip part is detected based on the reflected light. However, since the condition of the image of the chip part thus obtained varies depending on the reflectance or other properties of the chip part, it is difficult to realize uniform illumination conditions. In addition, since it is necessary to dispose the illumination apparatus in the periphery of the holding apparatus, there is the problem that the size of the apparatus as a whole becomes large.
In recent years, downsizing of parts has been achieved, and the current situation is that the outer diameter of the suction end of a suction nozzle is larger than the external size of a chip part. As a result, the above-described holding apparatus picks up an image of the external shape of the nozzle end portion simultaneously with the chip part. Therefore, an apparatus that can pick up an image of the external shape of even an extremely small chip part is demanded. To meet the demand, illumination apparatus disclosed in Japanese Patent Application Laid-Open No. 06-120699 has been proposed. This illumination apparatus is composed of a substantially ring-shaped semitransparent structure called a nozzle cap that contains a light emitting member such as a light emitting diode arranged in the outer circumferential portion. By arranging the illumination apparatus having the above-described structure in the vicinity of the end portion of the suction nozzle, image pickup processing can be performed for a chip part of a smaller size.
One exemplary application of the above-described holding apparatus is to bond a flexible printed circuit board (FPC) having flexibility to a head supporting member used in a flying type magnetic disk apparatus. Such a bonding process has been put into practice in view of demands for downsizing of magnetic heads, necessity for maintaining weight balance of magnetic head with high accuracy, demands for downsizing, and demands for an increase in density. Demands for that process are expected to increase further. In that process, a flexible printed circuit board placed on a waiting site is sucked to be held by a holding apparatus, and transferred onto a head supporting member that is fixedly held at a predetermined position. During the transfer process, the holding state of the flexible printed circuit board and the head supporting member is detected utilizing image processing. An adhesive has been applied at a predetermined portion of the head supporting member in advance, and the flexible printed circuit board is pressed against the adhesive with a predetermined positional relationship being maintained, so that the flexible printed circuit board and the head supporting member are securely adhered together.
A bonding method used for the aforementioned process in Japanese Patent Application Laid-open No. 2002-288812 has also been proposed. It is necessary for the holding apparatus used in that process to be provided with a member for pressing a predetermined portion of a flexible printed circuit board against adhesive in addition to the aforementioned suction nozzle. In addition, since the flexible printed circuit board is a member having a considerable length, a plurality of suction nozzles might be required as holding apparatuses in some cases. In that case, or in the case that for example the illumination apparatus disclosed in the aforementioned Japanese Patent Application Laid-Open No. 06-120699 is used, it is necessary to illuminate a specific portion on the flexible printed circuit board for which displacement amount or other factors is to be measured more efficiently in order to obtain a more clear image. However, it is considered that it would be difficult in some cases to arrange such an illumination apparatus at a position corresponding to the specific portion due to constraint of the structure.
On the other hand, a member having a pressing function is sometimes provided in addition to the suction nozzle. The illumination apparatuses disclosed in the aforementioned Japanese Patent Application Laid-Open No. 06-120699, Japanese Patent Application Laid-Open No. 62-060292, Japanese Patent Application Laid-Open No. 02-243232 or Japanese Utility Model Application Laid-Open No. 02-019436 might suffer from the problem that there might be hardly space for mounting such a member to spare. In other words, in the case that the holding apparatus is equipped with a plurality of suction nozzles for handling a single part such as a chip part, if the apparatus has a member for applying some effects (for example, a member for applying a load to the held part together with the suction nozzles), preferable effects may not be realized with use of conventional illumination apparatuses as they are.